Well my 4" Agri is now 12yrs old and the last couple of boiler inspections the inspector has mentioned there was a little bit of scale building up, so this year I felt it was time to give it a decent clean out.

I was just going to use some Citric acid powder disolved in water lob it and heater her up just like descaling our kettle but had a couple of reservations and the fact it would more than likely need to be steamed twice, once to heat the solution up and another to replace the boiler treatment, so looked about and found https://www.heritagesteamsupplies.co.uk/boiler-maintenance/boiler-descaling/dynamic-descaler/dynamic-descaler-5l.html however the price is a bit steep.

So looking further found these folks https://www.hitek-ltd.co.uk/hsl-eco-descale which appeared to be very similar and 1/2 the price, so grabbed some, the company was good to deal with and was happy with my usage and recommended I diluted it with 25%-50% with regular cold water and a 1hr treatment time, this is done totally cold so no need to fire it. So as I didnt know how bad it was went for a 25% addition of water to keep the concentration up.

Bewarned it says it might foam, well thats an understatement I pumped about a gallon in through the smoke box plug when it blew the pipe straight out and I had a 6foot jet of what was brown fizzing foam exit the bung, so yes it will foam I can only assume this proved that the boiler did have a reasonable amount of scale in it as it reacted so much with the descaler.After the brown jet subsided I was a little more careful adding the rest into the boiler a bit as a time. Anyhow after pretty much filling the boiler to the max I left it gently fizzing away for an hour and then drained it down, remembering to put it back into the containers it came in as it can be reused several times before the active ingredants do eventually die apparently and checking the used liquid it did seem to be still very active. Then its just a case of breaking out the presure washer and giving the inside a good blasting and then filling and draining her down twice to clean out any of the descaler, I then refilled with a nice strong solution of boiler treatment as I suspected the descaler would have stripped off any past protection it had and steamed her.

Anyhow my inspector came yesterday and had a good rumage with his camera and was a very happy bunny, certainly what I could see with the torch through the bungs showed a very clean and tidy boiler now

So for me this stuffs good stuff and the fact its reusable is great and I'll likely do it again with whats left over next year and continue until it stops working.

Yes. I also use the dynamic de-scaler. Crystal is a high road mileage and steam hours engine for her age.

As they say. It does what it says on the tin. I also purchased my own boroscope so I can keep an eye on what's going on inside. Helps when your father is a retired British Engine engineer boiler inspector. No he does not do my inspection as would be a conflict of interest.